This invention relates generally to equipment for maximizing efficiency of oil well pump systems and more particularly concerns shock absorbers for reducing or eliminating the damaging effects caused to such systems by fluid or gas pound.
In a publication entitled Recommended Practice for Care and Use of Subsurface Pumps, API Specification 11AR (RP11AR) 2nd Ed., March, 1982, the American Petroleum Institute identifies fluid pound and gas pound as two common pump problems, describes their damaging effects and offers solutions commensurate with prior art principles. Briefly stated, fluid and gas pound produce shock waves which will impose a severe shock load on an entire pumping system. Eventually these forces will manifest themselves as fatigue failure in the pumping unit base, structure, gear teeth and bearings, in the rod string, in various pump assembly parts and in the production tubing.
One solution proposed for fluid pound is to constrain the pounding effect to the early downstroke when pump plunger velocity is lower. Another solution offered is to match pump displacement to well productivity. Obviously, such solutions alleviate fluid pound damage at the expense of system efficiency and even require short term shut down periods. But this compromise is accepted because of the severity of the alternative.
The proposed solutions for gas pound include changing the subsurface separators and cleaning of pump fillage restrictions. While these solutions cause relatively modest system down time for changeovers, they are at best temporary, particularly when scale and undesirable solid particles increase separator and valve plugging problems.
Considering the relative inadequacy of the solutions proffered for such costly problems, it is clear that there is considerable room for innovation in the art. To this end, above-ground shock absorbers have been designed which provide limited beneficial results. In a typical example, the shock absorber is used to connect the oil well polished rod to its pumping unit. However, while this shock absorber diminishes the shock waves transmitted from the polished rod to the pumping unit and thus offers protection to the above-ground pump elements, the full impact of the waves is still transmitted all those pump system components located below the polished rod. Consequently, all below-ground pump elements remain subject to damage. Despite this improvement down time remains costly because, regardless of whether it is caused by an above-ground or a downhole failure, the system is still inoperable. It's not enough to solve half the problem. Perhaps this is why above-ground shock absorbers, some of which preceded the above referenced publication, were not identified as a solution by the American Petroleum Institute.
It is, therefore, an object of this invention to provide a shock absorber that will diminish or eliminate the problems caused by fluid and gas pound. Accordingly, it is an object of this invention to provide a shock absorber that is effective to reduce or absorb the shock waves generated throughout a pumping system under fluid and gas pound conditions. A related object of the invention is to provide a shock absorber located at or near the downhole pump so as to absorb shock waves prior to their transmission through the system to the surface. And it is an object of this invention to provide a shock absorber which is easily installed in and removed from a pump system.